The invention relates to organic light emitting diode (OLED) displays, and more particularly, to active matrix organic light emitting diode (AM-OLED) displays with thermal dissipation elements and fabrication methods thereof.
Among flat panel displays, organic light emitting diode (OLED) displays exhibit characteristics of self-emission, high brightness, wide viewing angle, high response and a simple fabrication process, making them the choice for the next generation of flat panel displays.
According to driving methods, organic light emitting diode (OLED) displays can be divided into two categories: passive matrix light emitting diode (PM-OLED) and active matrix organic light emitting diode (AM-OLED). Active matrix organic light emitting diode (AM-OLED) displays are more commonly used in flat panel display applications.
Conventionally, it is known that a passive matrix organic light emitting diode (PM-OLED) display is driven to display images by XY matrix electrodes, employing sequential line drive. If the number of scan lines is about hundreds, the required instantaneous brightness is several hundreds times the observed brightness. Thus, the corresponding instantaneously passed electrical current becomes several hundreds times the original passed electrical current. Therefore, larger and extreme heat generated result in increased operating temperature of the organic electroluminescent layers. Since the aging rate of organic electroluminescent layers is in direct ratio to the operating temperature thereof, however, the luminescent efficiency and lifetime of the organic electroluminescent device are thereby adversely affected.
The trend in organic electroluminescent display technology is for higher luminescent efficiency and longer lifetime. As a result, an active matrix organic electroluminescent device with thin film transistors is provided to solve the aforementioned problems. The active matrix organic electroluminescent device has panel luminescence with thin and lightweight characteristics, spontaneous luminescence with high luminescent efficiency and low driving voltage, and the advantages of increased viewing angle, high contrast, high-response speed, flexibility and full color. As the need for larger size display devices becomes increasing, higher resolution of the display devices grows, and active matrix organic electroluminescent devices become a major market trend.
The aforementioned AM-OLED devices can reduce current passing through the OLED, thereby preventing overheating generated by electric energy consumed. AM-OLED devices, however, typically use thin film transistors (TFTs) as switch devices through which a large amount of current passes. Since TFT channels are made of semiconductor materials such as amorphous silicon or polysilicon, resistance of the semiconductor materials can cause passing current to be converted into heat, increasing the operating temperature of the OLED device. As the operating temperature increases, for OLEDs with glass transition temperature (Tg) being about 100° C., it is apparent that the brightness of the OLED device depends on the OLED operating temperature. Such dependency directly affects the lifetime of the OLED device. That is, higher operating temperature can cause incremental degradation of the OLED device.
Accordingly, in order to dissipate heat generated by AM-OLED displays, U.S. Pat. No. 6,265,820, the entirety of which is hereby incorporated by reference, discloses a heat removal assembly includes a heat dissipating assembly for dissipating heat from the organic light emitting device, a heat transfer assembly for transferring heat from the top organic light emitting device to the heat dissipating assembly and a cooling assembly for cooling the organic light emitting display device. Furthermore, U.S. Pat. No. 5,821,692, the entirety of which is hereby incorporated by reference, discloses a cover having a rim engaging the supporting substrate is spaced from and hermetically encloses the organic electroluminescent device. A dielectric liquid having benign chemical properties fills the space between the cover and the organic electroluminescent device, providing both an efficient medium for heat transmission and an effective barrier to oxygen and moisture. Both disclosed OLED displays, however, are restricted to strength and thickness requirements. For example, the multi-level thermal dissipation structure increases total thickness of the OLED device. Furthermore, thermal dissipation fins weaken the strength of the OLED device, causing difficulties in assembly.